In this study we propose 1) to develop a new multisensor monitoring system associating a tri-axial accelerometer and a magnetometer to measure physical activity in free-living adults, 2) to perform its calibration and assess its validity in a series of activity tasks in comparison with the measure of energy expenditure by indirect calorimetry as the criterion measure, and with existing physical activity monitors (cardiofrequencemetry and accelerometers used either alone or in combination). Briefly the subjects will perform a series of standardized activity tasks of different intensities and a 30-min free physical activity period while wearing 6 MOTIONPOD(TM) and different commercial activity monitors. Physical activity energy expenditure will be measured using a metabolic gas analyser.